Typically, various movement mechanisms are used in the machine tool in order to move a workpiece (an object to be machined) and a tool for machining the workpiece to any relative positions.
For instance, linear movement mechanisms are provided in respective X axis, Y axis and Z axis to a support structure of a table on which the workpiece is placed or a support structure of a head to which the tool is attached in order to move the workpiece and/or the tool in three dimensions. Moreover, a rotary movement mechanism is used for changing a posture of the table and/or the head.
Each of the movement mechanisms includes: two relatively movable members (e.g., a guide member and a movement member movable along the guide member); a drive mechanism for moving the two members; and a guide mechanism for securing accuracy (guiding accuracy) of a movement direction or a movement axis.
Such a guide mechanism is required to have a high guiding accuracy, in other words, a geometrical accuracy showing that a linear movement is conducted in a line as straight as possible and a rotational movement is conducted in a circle as perfect as possible. Further, the guide mechanism is required to have a high load capacity, a low friction and a high damping performance (vibration absorption performance)
Specifically, the guiding accuracy of the guide mechanism affects a positioning accuracy of the two relatively movable members, thereby affecting a profile accuracy of a workpiece to be machined. The low friction of the guide mechanism affects the positioning accuracy along a movement axis, thereby affecting the profile accuracy of the workpiece to be machined. Moreover, vibration resistance affects damping of vibration between the two relatively movable members. Specifically, damping level of the vibration generating between the tool and the workpiece affects a machined surface roughness of the workpiece.
Recently, a hydrostatic pressure guide mechanism is used in the guide mechanism of the machine tool (see, for instance, Patent Literature 1 (JP-A-2004-58192)).
In a typical hydrostatic pressure guide mechanism such as the hydrostatic pressure guide mechanism disclosed in Patent Literature 1, a static pressure chamber (i.e., a concave portion into which an oil for supporting a static pressure load is supplied) is formed on one of a pair of slide surfaces. A lubricating oil is supplied into the static pressure chamber, whereby a load is transmitted by the static pressure to the other of the slide surfaces. In other words, only the lubricating oil intervenes between the pair of slide surfaces, so that the pair of slide surfaces are in non-contact with each other, thereby significantly reducing the slide resistance.
The hydrostatic pressure guide mechanism is exemplified by a hydrostatic pressure guide mechanism 8 shown in FIG. 28. The hydrostatic pressure guide mechanism 8 includes: a guide member 89 having a smooth guide surface; a movement member 81 having a slide surface 80 slidable on the surface of the guide member 89; an oil supply structure in a form of a concave portion 82 formed on the slide surface 80 of the movement member 81; an oil supply device 84 configured to supply oil in an oil tank 83 into the concave portion 82; and a hydraulic control valve 85 configured to control a pressure of an oil O in the concave portion 82 to be applied to the guide member 89.
The hydrostatic pressure guide mechanism 8 with this arrangement further includes a recovery portion 86 configured to recover all the oil O overflowing from the concave portion 82 (over the slide surface 80 of the movement member 81) into the oil tank 83 when load transmission is conducted between the slide surface 80 of the movement member and the guide surface of the guide member 89 in such a manner that the slide surface 80 and the guide surface of the guide member 89 are slidable on each other, in which the recovery portion 86 is configured to again supply the oil O recovered by the recovery portion 86 to the concave portion 82. Accordingly, in the hydrostatic pressure guide mechanism 8, the slide surface 80 of the movement member and the guide surface of the guide member 89 are slidable on each other by filling and circulating the oil O in the concave portion 82 and the recovery portion 86.
However, in the hydrostatic pressure guide mechanism 8, the oil O overflowing from the concave portion 82 is spread all over the slide surface 80 of the movement member 81 and subsequently overflows out of the slide surface 80 from the entire outer circumference of the movement member 81. For this reason, in the hydrostatic pressure guide mechanism 8, it is necessary to recover the oil O overflowing out of the slide surface 80 from the outer circumference of the movement member 81, so that the large recovery portion 86 is required.
Moreover, a large amount of the recovered oil cannot be returned through pipes, but is recovered through an open passage next to the guide surface or the slide surface 80. For this reason, a machined material, minute powders of a machined piece, dust and the like are likely to be mixed to degrade the oil in a short time. Moreover, the recovered oil is sheared by the guide mechanism to generate heat. The recovered oil heated to a high temperature is flowed along the slide surface 80 and the guide surface, thereby transmitting heat to a mechanical structure to thermally deform the structure.
Under such conditions, in the hydrostatic pressure guide mechanism 8, since it is necessary to fill the concave portion 82 and a large recovery portion 86 with the oil O, a large amount of the oil O is required when the guide surface of the guide member 89 and the slide surface 80 of the movement member 81 are slid on each other.
The same explanation applies to a heavy-weight support device configured to support a heavy weight in a manner capable of adjusting a position of the heavy weight in a horizontal direction with use of the hydrostatic mechanism.
As for the heavy-weight support device, a device having a seal portion on an outer circumference of the hydrostatic mechanism has been proposed (see Patent Literature 2: International Publication No. 2005/075859).
As shown in FIG. 29, a heavy-weight support device 9 includes: a support body 91 having a mount surface 90 on which a supported body 99 is mounted; an annular seal member 92 provided on the mount surface 90 of the support body 91; an oil supply structure that is positioned in a region surrounded by the seal member 92 on the mount surface 90 and provided in a form of a concave portion 94 communicating with an oil supply hole 93 for supplying the oil O onto the mount surface 90; and an oil supply device 96 configured to supply the oil in an oil tank 95 in the region surrounded by the seal member 92.
Moreover, the heavy-weight support device 9 with this arrangement further includes: valve mechanism 97 configured to stop supplying the oil O after a predetermined amount of the oil O is supplied in the concave portion 94; and a pressure release valve 98 configured to release the state where supplying the oil O in the concave portion 94 is stopped by the valve mechanism 97.
More specifically, the valve mechanism 97 includes a tapered portion 970 formed in the oil supply hole 93 and having a hole diameter decreasing toward the mount surface 90; and a valve body 971 configured to be inserted in the oil supply hole 93 and biased toward the mount surface 90. The valve body 971 includes: a contact portion 972 contactable with the tapered portion 970; and an extension portion 973 extending from the contact portion 972, a part of the extension portion 973 being positioned closer to the supported body 99 relative to the mount surface 90.
The pressure release valve 98 is configured to recover the oil O supplied in a region from the oil supply device 96 to the oil supply hole 93 into the oil tank 95.
Accordingly, in the heavy-weight support device 9 with this arrangement, when the supported body 99 is placed on the mount surface 90, the extension portion 973 of the valve body 971 is pressed by the supported body 99, whereby the tapered portion 970 is separated from the contact portion 972. When the oil O is supplied by the oil supply device 96 into the static pressure pocket P, which is a hermetically closed space on the mount surface 90 defined by the supported body 99 and the seal member 92, to cause the supported body 99 to be separated from the mount surface 90 (in other words, when a predetermined amount of the oil O is supplied into the static pressure pocket P), the contact portion 972 of the valve body contacts with the tapered portion 970 to stop supplying the oil O.
Further, when the oil O supplied in the region from the oil supply device 96 to the oil supply hole 93 is recovered into the oil tank 95 using the pressure release valve 98, an inner pressure of the static pressure pocket P is decreased to cause the extension portion 973 of the valve body 971 to be pressed on the supported body 99, whereby the tapered portion 970 is separated from the contact portion 972 to recover the oil O within the static pressure pocket P into the oil tank 95, so that the supported body 99 is supported on the mount surface in hermetic contact therewith.
Accordingly, when supporting the supported body 99, the heavy-weight support device 9 with this arrangement can keep a pressure of the oil O applied to the supported body 99 without continuously supplying the oil O into the static pressure pocket P.
Accordingly, with a modification of the hydrostatic pressure guide mechanism 8 according to the seal portion on the outer circumference and the supply and recovery of the oil as shown in above-described heavy-weight support device 9, it is expected that the supported body 99 can be supported without the need of a large amount of the oil O as described above in the hydrostatic pressure guide mechanism 8.
However, in the heavy-weight support device 9 described above in Patent Literature 2, since supplying the oil O is stopped after a predetermined amount of the oil O is supplied into the static pressure pocket P, a gap between the mount surface 90 and the supported body 99 cannot be adjusted.
The hydrostatic pressure guide mechanism according to the heavy-weight support device 9 has the same disadvantage.